Chapter: 11th Microbiology : Stains and Staining Methods

Classification of Stains

1. On the basis of origin, stains can be classified as natural and synthetic.
2. On the basis of chemical behavior, dyes are classified as acidic, basic and neutral.

Classification of Stains

1. On the basis of origin, stains can be classified as natural
and synthetic.

i. Natural stains:

·These
stains are obtained directly from natural products. For example, Haematoxylin
is obtained from the heartwood of a tree (Haematoxyloncampechianum).

·The
natural stains are used mainly for histological purposes.

ii. Synthetic stains:

·These
are artificially produced mainly from coal tar products and hence popularly
called coal-tar dyes.

·A
majority of stains used in microbiology are the synthetic type and manufactured
from Aniline. For example, Crystal violet, Safranin, Methylene blue and Acid
fuchsin.

2. On the basis of chemical behavior, dyes are classified as
acidic, basic and neutral.

·An
acidic dye is one in which the colour bearing ion, the chromophore, is an
anion.

·A
basic dye is one in which the colour bearing ion, the chromophore, is a cation.

·A
neutral dye is a complex salt of a dye acid with a dye base.

Acid dyes generally combine more strongly with cytoplasmic
(basic) elements of the cell, and basic dyes combine best with nucleic acid
(acidic) elements of the cell. Table 3.2 shows the chemical characteristics of
a stain or dye.